(a) Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has an electron emission source with an improved pattern to minimize the diffusion of electron beams, and enhance the screen color representation.
(b) Description of Related Art
Generally, the electron emission devices are classified into a first type where a hot cathode is used as an electron emission source, and a second type where a cold cathode is used as the electron emission source.
Among the second type electron emission devices there are field emitter array (FEA) types, surface conduction emitter (SCE) types, metal-insulator-metal (MIM) types, metal-insulator-semiconductor (MIS) types, and ballistic electron surface emitting (BSE) types.
With the FEA type, the electron emission source is formed with a material emitting electrons under the application of voltage, whereby the electrons strike the phosphors to emit light. The overall quality of the FEA type electron emission device is largely influenced by the characteristics of the electron emitters.
With the common FEA type, the emitters are formed on the rear substrate together with electrodes for controlling the electron emission of the emitters, such as cathodes and gate electrodes. An anode electrode and phosphor layers are formed on the surface of the front substrate facing the rear substrate.
FIG. 10 is a partial sectional view of a FEA typed electron emission device with front and rear substrates according to a prior art, and FIG. 11 is a plan view of the rear substrate shown in FIG. 10. As shown in the drawings, cathode electrodes 3 and gate electrodes 7 are formed on rear substrate 1 in a stripe pattern, and cross each other while interposing insulation layer 5. Openings 9 are formed at gate electrodes 7 and insulation layer 5 in respective crossed regions of cathode and gate electrodes 3, 7. Emitters 11 are formed on the surface portions of cathode electrodes 3 exposed through openings 9.
Anode electrode 15 is formed on the surface of front substrate 13 facing rear substrate 1, and red, green and blue phosphor layers 17R, 17G, 17B are formed on anode electrode 15 while interposing black layer 19.
Typically, phosphor layers 17R, 17G, 17B are formed in a stripe or slit pattern, which has a longitudinal side proceeding in the direction of the short axis of front substrate 13 (in the Y direction of the drawing). Each crossed region of cathode and gate electrodes 3, 7 corresponds to one of the phosphor layers while forming a sub-pixel, and three sub-pixels corresponding to the red, green and blue phosphor layers 17R, 17G, 17B collectively form one pixel.
In the above structure, openings 9 formed at gate electrodes 7 and insulation layer 5 as well as emitters 11 placed within openings 9 are formed in a circular shape. With circular-shaped emitter 11, when a predetermined driving voltage is applied to cathode electrode 3 and gate electrode 7 to emit electrons from emitter 11, the electron emission efficiency of emitter 11 is enhanced, thereby lowering the driving voltage.
However, with the structure where opening 9 and emitter 11 are circular-shaped, emitter 11 is spaced apart from gate electrode 7 at the same distance along the periphery thereof so that the electron beams from emitter 11 are diffused in a radial manner. Consequently, the electron beams emitted from emitter 11 may not land on the phosphor at the relevant sub-pixel, but may strike incorrect phosphors, thereby deteriorating the screen color representation.
Accordingly, in order to enhance the screen color representation through inhibiting the diffusion of electron beams, opening 9 and emitter 11 placed within the opening need to be reduced in their sizes, and electrodes for focusing the electron beams need to be formed separately. However, in this case, the structure of the device becomes complex which can result in processing difficulties.